Quantum-chemical study of substituent effects in meta and para substituted phenyl isothiocyanates in π-electronic approximation

HMO and PPP calculations of a series of meta and para substituted phenyl isothiocyanates have been carried out with the aim of study of the substituent effects on the reaction centre of these compounds. The transition state of nucleophilic addition reaction of phenyl isothiocyanates has been approximated by two models, and the calculated localization energies at the carbon atom of NCS group have been investigated with respect to logarithms of rate constants of the nucleophilic reaction and to σ constants. Whereas in the former relation (i.e. localization energies vs log k) rough trends only have been found, the latter one (i.e. localization energies or π-electron densities vs σ) shows statistically significant linear correlations.